Sputtering target, method of making same, and high-melting metal powder material

ABSTRACT

There is provided a method of making a high-melting metal powder which has high purity and excellent formability and, particularly, of a metal powder of spherical particles made of Ta, Ru, etc. having a higher melting point than iron. There is also provided a target of high-melting metal or its alloy, which is made by the sintering under pressure of these powders and which has high purity and a low oxygen concentration and shows high density and a fine and uniform structure. A powder metal material mainly composed of a high-melting metal material is introduced into a thermal plasma into which hydrogen gas has been introduced, thereby to accomplish refining and spheroidizing. Further, an obtained powder is pressed under pressure by hot isostatic pressing, etc.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a sputtering target comprising arefractory metal material, such as Ta and Ru, particularly for use inthe manufacture of semiconductor LSIs and a method of making thesputtering target.

[0002] Conventionally, Al and Al alloys have been used as wiringmaterials for semiconductor LSIs. However, with the recent highintegration design, minute design and high-speed design of operation ofLSIs, it has been examined to use Cu which has higher electromigration(EM) resistance and higher stress migration (SM) resistance and provideslow electric resistance. However, Cu readily diffuses into the SiO₂ ofinterlayer dielectric film and also into an Si substrate and, therefore,it is necessary to enclose Cu wiring with a diffusion barrier layer. Asthe barrier materials for Cu, a TaN film formed by performing reactivesputtering in an atmosphere of argon and nitrogen through the use of aTa sputtering target and a Ta—X—N film formed by performing reactivesputtering through the use of a Ta—X alloy target are considered good.For this reason, Ta and Ta—X alloy sputtering targets for barrier metalapplication for semiconductor LSIs have been developed.

[0003] On the other hand, in a DRAM and FeRAM of semiconductor memory, aPt film formed by the sputtering of a Pt target has so far been used asa capacitor electrode. However, with further large capacity design, itis being examined to use an Ru film formed by performing the sputteringof an Ru target as a capacitor electrode.

[0004] In the manufacture of targets of the above high-melting metals ortheir alloys (Ta, Ta alloys, Ru, etc.), any one of a melting-plasticworking process and a powder sintering process can be selected, whilethe powder sintering process is most suited. Reasons for this aredescribed below.

[0005] First, although the hot plastic working of Ta is possible, it isvery difficult to make crystal grains uniform and fine. According toresults of an investigation performed by the present inventors,coarsened crystal grains of a target are one of the major causes ofgeneration of particles during sputtering. Recently, addition of a thirdalloying element to Ta—N has been proposed in order to improve thebarrier property of a Ta—N film. Si and B are mentioned as such alloyingelements and it is said that a Ta—X—N film formed by the reactivesputtering of a Ta—X target (X: alloying element such as Si and B)becomes amorphous, thereby improving the barrier property. However, aTa—X alloy target raises a problem that plastic working is impossibledue to the segregation by solidification and the formation ofintermetallic compounds.

[0006] On the other hand, in the case of Ru, manufacture by plasticworking is impossible because this metal does not have plasticworkability. Therefore, it can be said that the superiority of thepowder sintering process, including an advantage of yield improvement inthe near-net-shape manufacture of targets, is clear as a method ofmaking high-melting metal targets of Ta, Ta—X alloys and Ru.

[0007] Incidentally, with the recent high integration design of LSIs andminute design of devices, requirements for a reduction of impurities inmaterials for thin films have become very severe. In particular, fortransition metals (Fe, Ni, Cr, etc.) and alkali metals (Na, K, etc.)which are considered to have a great adverse effect on the performanceof devices, it is required to reduce such impurities to the order ofppb, and for radioactive elements (Th, U, etc.) to the order of ppt.Furthermore, for other low-melting metal impurities also, it is requiredto lower their concentrations and, as a result, it is necessary toincrease purity to not less than 99.999%. In addition, in order toimprove the thermal stability of barrier films, the interface electriccharacteristic of DRAM capacitor electrode films, etc., it is alsorequired to lower oxygen concentrations to not more than 100 ppm.

[0008] Ta powders that can be industrially supplied are conventionallyobtained by an ingot crushing process after performing the EB melting ofa low-purity Ta raw material, and their purity is only a level of 4N atthe most. On the other hand, the following method, for example, isadopted as a process for industrially making Ru. Caustic potash andpotassium nitrate are added to crude Ru, thereby converting Ru intosoluble potassium ruthenate. This salt is extracted in water and isheated during chlorine gas injection under the formation of RuO₄, whichis then collected in dilute hydrochloric acid containing methyl alcohol.This liquid is evaporated and dried, and is then calcined in an oxygenatmosphere to form RuO₂, with the result that Ru metal is finallyobtained by reduction under heating in hydrogen. Commercial Ru powdersmade by this method contained low-melting metal impurities, alkalimetals, and residues of halogen elements such as Cl and hence could notmeet the purity required of capacitor electrode films. Moreover, powdersmade by this method were coral-like porous agglomerates and had very lowpacking densities in the case of sintering.

[0009] In order to increase the purity of Ta and Ru targets, there havebeen proposed methods of refining the above raw material by EB melting,more concretely, a method which involves plastic working of an Ta ingotobtained by the EB melting and a method of machining an Ru ingotobtained by the EB melting into a target in a casting condition thereof.For example, JP-A-3-197940 discloses a method of plastically working anTa ingot obtained by EB-melting. Also, JP-A-6-264232 discloses a methodof performing plastic working and heat treatment of Ta after the EBmelting thereof. Further, JP-A-11-61392 discloses a method of machiningan ingot obtained by the EB melting of an Ru raw material and using itin a casting condition thereof.

[0010] High purity may be realized by using the methods disclosed in theabove literature. In those cases, however, as mentioned above, there isa fear of causing a coarse or nonuniform of the microstructure at thestage of plastic working of an ingot. Further, with a material in acasting condition, the presence of a large number of pores and castingdefects cannot be neglected. In addition, in the melting methods, it isimpossible to perform near-net-shape forming and the yield of noblemetals is low. In other words, it can be said that the melting methodsproposed in the above literature are an unavoidable choice because highpurity and low oxygen concentrations could not be realized in the powdersintering method.

[0011] In general, it is difficult to sinter the refractory metals (moreconcretely, metals each having a melting point higher than that of iron)to high density in order to increase the density of a sintered compact,pressure sintering is one of effective methods. Because metal powdersare filled into a capsule and then the capsule with packing powders issintered, the packing condition of a raw material powder is an importantfactor. In hot isostatic press (HIP), increasing the packing densityaccelerates an increase in the density of a sintered compact and reducesabnormal shrinkage during sintering and sinter cracks, resulting in anincrease in yield. In other words, in performing sintering underpressure, packing a raw material powder at a high density and uniformpacking bear an important meaning. It is well known that thespheroidizing treatment of a raw material powder is effective inrealizing such high packing density and uniform packing. However, incase of using a crushed Ta powder and a coral-like Ta powder, thepacking density is low and, therefore, the optimization (spheroidizing)of these powder shapes is also an important problem in the sinteringtechnology of targets.

[0012] As a method for realizing the spheroidizing of a high-meltingmetal powder, JP-A-3-173704 discloses a method of producing a sphericalTa powder by Plasma Rotating Electrode Process (PREP) treatment, i.e.,by bringing a thermal plasma into contact with a rotating electrode andthereby causing an electrode material to melt and splash. Under thismethod, however, the thermal plasma is given with the purpose of onlyspheroidizing performed by heating and melting, and the effect ofpurification of powder cannot be expected.

SUMMARY OF THE INVENTION

[0013] Therefore, an object of the invention is to provide a method ofmaking a high-melting metal powder which has high purity and which isexcellent in compacting and sintering, and particularly a method ofmaking a spherical powder made of Ta, Ru, etc. having a higher meltingpoint than that of iron. Another object of the invention is to provide atarget made of high-melting metals or its alloy, which is producted bysintering these powders under pressure and which has high purity and lowoxygen concentrations and besides shows high density and a fine anduniform micro-structure.

[0014] In order to attain the above objects, the present inventors haveconducted research energetically and found out that by applying thermalplasma treatment to a raw material powder, it is possible to spheroidizea high-melting metal powder and, at the same time, to obtain high purityand low oxygen concentrations. Further, the inventors have found outthat by performing sintering under pressure through the use of thispowder which is spherical and has high purity and a low oxygenconcentration, it is possible to increase packing density, with theresult that it is possible to obtain a sintered powder compact suitablefor sputtering targets, which has high purity and a low oxygenconcentration and besides shows a high density and a uniform and finemicro-structure.

[0015] In the method of making a target according to the invention, byintroducing a powder mainly composed of a high-melting metal into athermal plasma flame, refining and spheroidizing are performed and anobtained powder is sintered under pressure. As a result of this process,it is possible to obtain a sputtering target which has high purity and alow oxygen concentration and besides shows high density and a uniformand fine micro-structure.

[0016] Further, in the method of making a target according to theinvention, a powder is introduced into a thermal plasma into whichhydrogen gas has been introduced. As a result of this process, it ispossible to obtain a sputtering target having chemical composition whichhas high purity and a low oxygen concentration and besides shows highdensity and a uniform and fine micro-structure.

[0017] Also, in the method of making a target according to theinvention, the sintering under pressure is hot isostatic pressing. As aresult of this process, it is possible to obtain a sputtering targetwhich shows high density and a uniform and fine micro-structure.

[0018] The sputtering target according to the invention comprises asintered powder compact with a relative density of not less than 99%, apurity of not less than 99.999% and an oxygen concentration of not morethan 100 ppm. As a result of this matter, a thin film obtained bysputtering through the use of this target has high purity and is uniformso as to improve the reliability of products.

[0019] Also, the sputtering target according to the invention isobtained by performing the sintering under pressure of a powder obtainedby introducing a powder material mainly composed of a high-melting metalinto a thermal plasma. As a result of this process, a thin film obtainedby performing sputtering through the use of this target has high purityand is uniform, improving the reliability of products.

[0020] Also, the sputtering target according to the invention isobtained by introducing a powder into a thermal plasma into whichhydrogen gas has been introduced. As a result of this, a thin filmobtained by performing sputtering through the use of this target hashigh purity and is uniform so as to improve the reliability of products.

[0021] Also, in the sputtering target according to the invention, theshape of particles of the powder introduced for sintering under pressureis spherical or analogous to a sphere. As a result of this, the targetshows high density and a uniform and fine micro-structure, and theuniformity of a thin film obtained by performing sputtering through theuse of this target increases.

[0022] Further, in the sputtering target according to the invention, theabove high-melting metal material is Ta. As a result of this matter, itis possible to obtain a Ta target which has high purity and a low oxygenconcentration and shows high density and a uniform and finemicro-structure, and by using this Ta target, it is possible to obtain aTa thin film which has high purity and is uniform.

[0023] Further, in the sputtering target according to the invention, theabove high-melting metal is Ru. As a result of this matter, it ispossible to obtain an Ru target which has high purity and a low oxygenconcentration and shows high density and a uniform and finemicro-structure, and by using this Ru target, it is possible to obtainan Ru thin film which has high purity and is uniform.

[0024] Further, the high-melting metal powder according to the inventionhas a purity of not less than 99.999% and an oxygen concentration of notmore than 100 ppm and the shape of particles of the high-melting metalpowder is spherical or analogous to a sphere. By performing pressuresintering with the use of this powder, the packing density of the powderincreases and it is possible to obtain a formed powder compact whichshows high density and a uniform and fine micro-structure.

[0025] Further, the high-melting metal powder material according to theinvention is obtained by introducing a powder mainly composed of ahigh-melting metal into a thermal plasma. As a result of this process,the obtained high-melting metal powder becomes a powder of sphericalparticles which has high purity and a low oxygen concentration as achemical composition, and by performing pressure sintering through theuse of this powder, it is possible to obtain a formed powder compactwhich has high purity and a low oxygen concentration and besides showshigh density and a uniform and fine micro-structure.

[0026] Further, the high-melting metal powder according to the inventionis obtained by introducing a powder into a thermal plasma into whichhydrogen gas has been introduced. As a result of this process, theobtained high-melting metal powder material becomes a powder ofspherical particles which has high purity and a low oxygenconcentration, and by performing pressure forming through the use ofthis powder, it is possible to obtain a formed powder compact which hashigh purity and a low oxygen concentration and besides shows highdensity and a uniform and fine micro-structure.

[0027] As mentioned above, the greatest feature of the invention residesin the fact that a powder mainly composed of a metallic material with ahigher melting point than iron, particularly Ta or Ru, is introducedinto a thermal plasma, thereby to obtain a high-melting metal powdermaterial which has high purity and a low oxygen concentration and theshape of whose particles is spherical or analogous to a sphere. When aradio-frequency (RF) thermal plasma is specifically selected from amongthermal plasmas and used as a heat source, the range of the thermalplasma widens and it is possible to suppress the contact of the powderwith other substances during treatment. This is most favorable forobtaining high purity.

[0028] Further, by introducing hydrogen into a thermal plasma gas, it ispossible to remarkably improve the evaporation of impurities and theeffect of the reduction of oxygen owing to the generation of ions andexcited atoms of hydrogen.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a schematic view of the structure of a thermal plasmatreatment apparatus used in the invention.

[0030]FIGS. 2A and 2B are micrographs obtained by a scanning electronmicroscope for showing changes in the shape of Ta powder particlesbefore and after the thermal plasma treatment.

[0031]FIGS. 3A and 3B are micrographs obtained by a scanning electronmicroscope for showing changes in the shape of Ru powder particlesbefore and after the thermal plasma treatment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Embodiments of the invention will be described below. Withreference to an apparatus shown in FIG. 1, a procedure for performingthe thermal plasma treatment of a powder will be explained through theuse of the above thermal plasma treatment apparatus for powdertreatment.

[0033] 1. A raw material powder (110) is charged into anelectro-magnetic powder feeder (hereinafter referred to simply as apowder feeder) and a thermal plasma generator comprising a thermalplasma torch (not shown in the figure) and a chamber (106) is evacuatedto a vacuum of up to 10-3 Pa.

[0034] 2. When a thermal plasma has caught fire and a plasma gas (120)has been introduced at a predetermined flow rate, input power is set toa predetermined numerical value, thereby to establish a plasmahigh-temperature zone (105) in a stable manner.

[0035] 3. The raw material powder (110) is introduced by transportationon a carrier gas from the powder feeder (101) via a nozzle (102) intothe plasma high-temperature zone (105) having a temperature between5,000 to 10,000° K. At this time, the raw material powder (110) ismelted and becomes spherical due to the action of the surface tension ofthe liquid phase of the metal.

[0036] 4. The powder treatment is performed by introducing the rawmaterial powder (110) into a thermal plasma region (not shown in thefigure).

[0037] 5. After the completion of the treatment, the plasma gas (120)and power source are stopped and powder after the treatment is recoveredfrom a powder recovery can (108). It is possible to perform the recoveryboth in a protective gas and in the air.

[0038] In the thermal plasma high-temperature zone (102), the rawmaterial powder (110) is melted and becomes spherical due to the actionof the surface tension of the metal, and as a result of this process,the shape of the powder particles after the treatment becomes spherical.

[0039] Further, oxides and low-melting impurities contained in the rawmaterial powder (110) evaporate in the thermal plasma high-temperaturezone (105) because their vapor pressures are higher than those of Ta andRu. As a result of this condition, the purity of the raw material powder(110) increases and, at the same time, its oxygen concentrationdecreases. However, the pressure of the plasma gas used here is almostatmospheric pressure and hence the effect of the evaporation ofimpurities is not great with an argon thermal plasma treatment alone. Insuch cases, if hydrogen is introduced thereinto, it is possible tofurther lower the oxygen concentration by the reduction reaction ofhydrogen ions, excited atoms, etc. In the invention also, theintroduction of hydrogen gas enables the effect of the evaporation ofimpurities to be remarkably improved.

[0040] Hot pressing or hot isostatic pressing (HIP) is performed throughthe use of a high-melting metal powder obtained in the manner shownabove. In HIP, in particular, a powder is packed in a capsule made ofcarbon steel on the bottom of which a piece of Mo foil is laid, and HIPis performed after deaeration and sealing in a vacuum. It is desirablethat this powder be sintered under pressure at a temperature of not lessthan 1100° C. and at a pressure of not less than 50 MPa. Next, the abovesintered powder compact is subjected to machining or surface grindingand is bonded to a packing plate, thereby to complete a target.

[0041] In conventional powders, the shrinkage during sintering was greatbecause of their low packing densities and it was necessary to considerextra thicknesses and diameters in order to ensure target sizes. Inaddition, yields were low because of abnormal shrinkage and sinteringcracks. It has become apparent that, in contrast to this matter, byimproving packing density through the use of a powder of sphericalparticles obtained with the aid of a thermal plasma as mentioned above,for example, in a case where a target with a size of 350 to 400 mm indiameter×10 mm in thickness is to be made, it is possible to reducepowder consumption by 10 to 30% in comparison with conventional powders.

EXAMPLE 1

[0042] Examples of the invention will be explained below. The treatmentof Ta powders was actually carried out through the use of an apparatusof the structure shown in FIG. 1. The Ta raw material powders used inthe treatment and thermal plasma treatment conditions are shown inTable 1. Further, with respect to changes in the shape of powderparticles before and after the thermal plasma treatment, micrographs ofSpecimen 3, as an example, obtained by a scanning electron microscopeare shown in FIGS. 2A and 2B. FIG. 2A is a photograph of a raw materialpowder (before the thermal plasma treatment) and FIG. 2B is a photographof Specimen 3 (after thermal plasma treatment).

[0043] Next, the powder after the thermal plasma treatment was packed inan HIP can and the packing density at that time was measured. The resultof the measurement is shown in Table 1. Further, a Ta target with a sizeof 350 mm in diameter×10 mm in thickness was fabricated from the powderof spherical particles under the sintering conditions of 1350° C.-155MPa-1 hour. The packing density was measured, and the result of themeasurement is also shown in Table 1.

[0044] Further, an impurity analysis of the sintered Ta compact was madewith the aid of a GD-MS (glow discharge-mass spectrometer). The resultof the analysis is shown in Table 2. Incidentally, in order to makeclear the effects of the thermal plasma treatment on the packing densityand chemical composition of the sintered powder compact, the samemeasurements as mentioned above were carried out also for the rawmaterial powder not subjected to the thermal plasma treatment, and theresults of these measurements are also shown in Tables 1 and 2.

[0045] The results of the above examination will be looked over. First,it is apparent from Table 1 that each of Specimens 1 to 3 subjected tothe thermal plasma treatment, has a packing density of not less than 60%in an HIP can and a sintering density of almost 100%, both showing asubstantial increase in comparison with the raw material powder that isa comparative example. This is because, as shown in FIGS. 2A and 2B, theshape of powder particles became spherical due to the thermal plasmatreatment.

[0046] As made clear from the result shown in Table 2, the purity of Tais increased from a level of 3N to levels of 4N and 5N by the thermalplasma treatment. From the foregoing it has become apparent that a Tatarget obtained from a Ta powder subjected to the thermal plasmatreatment by pressure sintering is most suited to the formation of a TaNfilm by reactive sputtering.

EXAMPLE 2

[0047] Chemically processed powder Ru was examined in the same manner aswith Example 1. The Ru raw material powders and thermal plasma treatmentconditions as well as measurement results of HIP can packing density andsintering density are shown in Table 3. Further, with respect to changesin the shape of powder particles before and after the thermal plasmatreatment, micrographs of Specimen 6, as an example, obtained by ascanning electron microscope are shown in FIGS. 3A and 3B. FIG. 3A is aphotograph of a raw material powder (before the thermal plasmatreatment) and FIG. 3B is a photograph of Specimen 6 (after thermalplasma treatment). Further, an Ru target with a size of 400 mm indiameter×10 mm in thickness was fabricated from the powder of sphericalparticles. An impurity analysis of the Ru target after sintering wasmade, and the result of the analysis is shown in Table 4.

[0048] From the results shown in Table 3, it is apparent that each ofSpecimens 4 to 6 subjected to the thermal plasma treatment, has an HIPcan packing density of not less than 60% and a sintering density ofalmost 100%, both showing a substantial increase in comparison with theraw material powder that is a comparative example. This is because, asshown in FIGS. 3A and 3B, the shape of powder particles became sphericaldue to the thermal plasma treatment.

[0049] From the result shown in Table 4, it is apparent that the purityof Ru is increased from a level of 3N to levels of 4N and 5N by thethermal plasma treatment. From the foregoing it has become apparent thatan Ru target obtained from an Ru powder subjected to the thermal plasmatreatment by pressure sintering is most suited to the formation of an Rufilm by sputtering. TABLE 1 Compara- tive example (Raw material SpecimenSpecimen Specimen powder) 1 2 3 Plasma Particle 250-325 250-325 325-425250-325 treat- size of raw meshes meshes meshes meshes ment materialcondi- powder tions Plasma — 45 kW 28 kW 40 kW power Composition — ArAr + 8% Ar + 30% of plasma H₂ H₂ gas Flow rate — 80 75 85 of plasma gas(1/min) Flow rate — 10 10 15 of carrier gas (1/min) Sinter- HIP can 46.862.5 63.1 82.7 ing packing density Sintering 96.3 99.6 99.8 99.9 density

[0050] TABLE 2 Comparative example (Raw material Specimen SpecimenSpecimen powder) 1 2 3 Na 0.785 0.681 0.008 <0.001 Mg 0.624 0.411 0.0270.018 Al 3.761 2.522 0.201 0.146 Si 10.192 7.804 0.603 0.410 P 0.2200.321 0.227 0.255 S 0.591 0.580 0.041 0.034 Cl 2.572 0.726 0.010 0.005 K3.871 1.073 0.027 0.001 Ca 1.442 0.516 0.013 0.007 Ti 4.433 4.162 0.3570.041 V 0.020 0.021 <0.007 <0.004 Cr 13.644 11.956 0.976 0.759 Mn 0.9321.033 0.352 0.366 Fe 38.431 37.523 0.970 0.178 Co 0.827 0.786 0.0340.026 Ni 4.700 3.384 0.803 0.715 Cu 6.812 4.920 0.621 0.490 Nb 0.5590.587 0.512 0.523 Mo 4.037 4.121 1.136 0.980 Ru 0.152 0.171 0.144 0.130Pb 0.179 0.195 0.083 0.067 In 0.251 0.264 0.141 0.102 Ir 0.053 0.0710.059 0.056 Th 14.930 3.726 27.417 20.307 ppb ppb ppt ppt U 19.46516.357 53.060 41.150 ppb ppb ppt ppt C 23.716 <20 <10 <10 N 1.504 1.3160.882 0.627 O 1450 1410 96 38 Purity of 99.98% >99.99% >99.999% >99.999%Ta

[0051] TABLE 3 Compara- tive example (Raw material Specimen SpecimenSpecimen powder) 4 5 6 Plasma Particle 200-325 100-250 200-325 200-325treat- size of raw meshes meshes meshes meshes ment material condi-powder tions Plasma — 45 kW 28 kW 40 kW power Composition — Ar Ar + 8%Ar + 30% of plasma H₂ H₂ gas Flow rate of plasma — 80 75 85 gas (1/min)Flow rate of carrier — 10 10 15 gas (1/min) Sinter- HIP can ing packing33.3 65.2 66.2 65.8 density Sintering 96.7 99.7 99.9 99.9 density

[0052] TABLE 4 Comparative example (Raw material Specimen SpecimenSpecimen powder) 4 5 6 Na 2.383 1.904 0.117 0.024 Mg 2.300 1.832 0.2130.078 Al 5.837 4.983 0.640 0.182 Si 3.409 2.114 0.175 0.100 P 0.6440.563 0.272 0.061 S 0.121 0.101 0.041 0.080 Cl 61.504 6.033 0.780 0.064K 4.370 1.754 0.061 0.004 Ca 1.363 0.712 0.032 0.002 Ti 1.156 0.9820.084 0.040 V 0.121 0.118 0.087 0.074 Cr 0.504 0.511 0.027 0.018 Mn0.123 0.112 0.063 0.044 Fe 6.548 5.861 0.143 0.110 Co 1.278 1.004 0.2540.107 Ni 2.693 1.508 0.621 0.087 Cu 2.771 1.019 0.276 0.061 Nb 0.0340.045 0.042 0.041 Zr 0.787 0.658 0.094 0.035 Mo 0.071 0.067 0.078 0.070Rh 0.304 0.401 0.417 0.409 In 2.804 2.201 0.409 0.006 Sn 3.565 1.8700.186 0.207 Sb 2.380 1.306 0.122 0.098 Ta 0.227 0.229 0.374 0.391 W0.102 0.110 0.131 0.137 Th 77.234 73.701 <0.101 <0.101 ppt ppt ppt ppt U385.720 250.144 <98.289 <71.143 ppt ppt ppt ppt C <2 <2 <2 <12 N <0.2<0.2 <0.2- <0.2 O 1278 87 21 <10 Purity of99.95% >99.99% >99.999% >99.999% Ru

[0053] As mentioned above, according to the invention, by performing thethermal plasma treatment through the use of a thermal plasma into whichhydrogen is introduced, an increase in purity, a decrease in oxygenconcentration, and the spheroidizing of high-melting metal powdermaterials of Ta, Ru, etc. can be simultaneously realized. Furthermore,by performing the sintering under pressure of an obtained powder, it ispossible to realize a Ta or Ru target which shows high density and afine and uniform micro-structure and which has high purity and a lowoxygen concentration and to obtain an optimum sputtered thin film.

What is claimed is:
 1. A method of refining a metal powder comprisingthe steps of: passing a powder metal through a thermal plasma into whicha hydrogen gas is introduced; and performing to high-purify it.
 2. Amethod of making a target comprising the steps of: introducing a powdermaterial mainly composed of refractory metal into a thermal plasma,thereby to perform refining and spheroidizing; and sintering an obtainedpowder under pressure.
 3. A method of making a target according to claim2, wherein said powder material is introduced into a thermal plasmaflame into which hydrogen gas has been introduced.
 4. A method of makinga target according to claim 2, wherein said sintering under pressure ishot isostatic pressing.
 5. A method of making a target according toclaim 2, wherein the powder material mainly composed of refractory metalis introduced into the thermal plasma into which a hydrogen gas isintroduced, thereby to perform refining and spheroidizing; and sinteringthe obtained powder under hot isostatic pressing.
 6. A sputtering targetcomprising a sintered powder compact with a relative density of not lessthan 99%, a purity of not less than 99.999%, and an oxygen concentrationof not more than 100 ppm.
 7. A sputtering target which can be obtainedby performing the pressure sintering of the powder obtained byintroducing a powder material mainly composed of a refractory metal intoa thermal plasma.
 8. A sputtering target according to claim 7, whereinsaid target can be obtained by introducing a powder into a thermalplasma flame into which hydrogen gas has been introduced.
 9. Asputtering target according to claim 7, wherein a shape of particles ofsaid powder introduced for pressure sintering is spherical or analogousto a sphere.
 10. A sputtering target according to 7, wherein said metalmaterial is Ta.
 11. A sputtering target according to 7, wherein saidmetal material is Ru.
 12. A sputtering target according to claim 7,wherein said target can be obtained by performing the pressure sinteringof the powder obtained by introducing a powder material into a thermalplasma into which a hydrogen gas has been introduced, said powdermaterial being mainly composed of Ta and Ru and the shape of particlesof said powder material being spherical or analogous to a sphere.
 13. Arefractory metal powder material, said powder having a purity of notless than 99.999%, an oxygen concentration of not more than 100 ppm, andhaving a shape of a sphere or analogous thereto.
 14. A refractory metalpowder material according to claim 13, wherein said powder material canbe obtained by introducing the powder material mainly composed of arefractory metal into a thermal plasma flame.
 15. A refractory metalpowder material according to claim 13, wherein said powder material canbe obtained by introducing said powder material into a thermal plasmaflame into which hydrogen gas has been introduced.
 16. A refractorymetal powder material according to claim 13, wherein said powdermaterial mainly composed of a refractory metal is introduced into athermal plasma flame into which hydrogen gas is introduced, a purity ofthe powder material is not less than 99.999%, an oxygen concentrationthereof not more than 100 ppm, and a shape of said powder material is asphere or analogous thereto.